Process for bleaching hair by laser irradiation, and device

ABSTRACT

The present invention provides a process for bleaching a lock or portion of lock of hair, at least partially, by irradiation of the lock using a laser beam in the form of pulses, and a device for implementation of same.

The invention relates to a process for bleaching hair. More precisely,the subject of the invention is a process for bleaching hair by laserirradiation, and a device for implementing this process.

It is known that, in order to bleach or lighten the colour of hair, itis conventional to use a chemical treatment with the aid of an oxidizingagent, such as hydrogen peroxide or persalts, which destroys at leastpart of the natural and/or artificial colouring substances present inthe hair.

The conventional method of chemically bleaching hair requires the use ofrelatively powerful and/or concentrated oxidizing agents which have theeffect of degrading not only the colouring substances but also thekeratinous fibre of the hair. The result of this is that hair bleachedin this way is fragile and must subsequently be treated with care.

For these reasons, it is impossible for various cosmetic treatments suchas for example the permanent-reshaping treatment used for natural hairto be applied to such bleached hair, which treatment consists inapplying, to the hair, a reducing agent at relatively high pH values andthen an oxidizing agent, and these agents have markedly aggressiveeffects on the keratinous fibre of the hair. In fact, application of aconventional permanent-reshaping treatment on a bleached head of hair bychemical route causes irreversible degradation and even hair breakages.

Moreover, it is known that a large proportion of people desire to have aso-called "highlighted" head of hair, that is to say a head of hairwhich has not been totally bleached but in which only certain locks ofhair have been bleached. This involves a so-called "highlighting"operation. The case of highlighted heads of hair is particularly trickysince natural hair and highly bleached hair are then encountered on thesame head of hair.

The present invention makes it possible to remedy these variousdrawbacks thanks to a process for bleaching hair by irradiation using alaser beam, under special conditions which make it possible to obtain,on all types of hair, whether coloured naturally or artificially,bleaching of easily controllable intensity, without appreciabledegradation of the keratinous fibre, and the treatment may be quiterapid. This process is particularly well suited for obtaining ahighlighted head of hair. Furthermore, the hair bleached in this waykeeps the mechanical and physico-chemical properties that it had beforebleaching. It may, for example, be subjected immediately to apermanent-waving treatment with conventional permanent-wavingcompositions.

The theoretical possibility of bleaching hair with laser radiation wasmentioned in the publication Tech. News, Laser Focus, Vol. 19, No. 9,p.26, September 1983. Furthermore, in U.S. Pat. No. 4,792,341, anexperimental device has been described which makes it possible to studythe destruction of the melanin of the hair using laser radiation. Infact, this U.S. patent describes neither a process nor a device makingit possible, in practice, to apply the laser irradiation to thebleaching of hair.

It has now been discovered that it is possible to bleach locks of hairwhatever their original (natural or artificial) colour, withoutdegradation of the keratinous fibre, by successively subjecting parts ofthe locks of hair to be treated to irradiation by a laser beam as longas a laser-radiation power is chosen which is suitable for the type ofhair to be bleached.

Studies on isolated hairs of various origins (European, Japanese,Mexican and Scandinavian natural hair) have made it possible to studythe luminous power necessary to obtain good bleaching of hair withoutdegradation of the keratinous fibre, with a single laser pulse (one-shotfiring). It has been observed that very dark (Japanese or Mexican) hairdoes not become sufficiently bleached in depth or shatters under theirradiation when the power per unit area is further increased, for agiven pulse duration. By using a peak power less than the highest peakpower which, in one-shot firing, for the pulse duration used and for thetype of hair under study, does not cause shattering of the keratinousfibre, successive shots were subsequently carried out, in sequences, onthe same area of the isolated hairs treated. It has been discovered thatthe isolated hairs, even very dark hairs of the Japanese or Mexicantype, could be bleached without damage by lowering the peak power inthis way and by carrying out several successive passes on a treatedarea, thereby making it possible to bleach firstly the surface layersand then the deeper layers, and eventually the hairs may be completelybleached.

Similar studies performed on locks of hair have enabled it to beestablished that it is possible to bleach hair arranged in locks, aslong as a laser-radiation power suitable for the type of hair treated isselected. This power must be sufficient to degrade or destroy themelanin but must not exceed a certain threshold. It has been discoveredthat the darker the natural colour of hair, the lower this threshold hasto be. This therefore leads to the surprising result that the moredifficult the hair is to bleach, the more the laser-radiation power hasto be moderated.

As will be obviously apparent to those skilled in the art, it is in factthe energy delivered to the particles of melanin, over a sufficientlyshort time duration, which has to be high enough to degrade or destroythe melanin. In reality, it is therefore the energy density deliveredper unit area, in a sufficiently short time, which has to reach athreshold high enough for the hair to be able to be bleached. In thepresent application, when one speaks of "power" or "peak power", itshould be understood that this is a language simplification as it is infact the energy delivered during each pulse which is important, and itis therefore necessary to take into account the duration of the pulsewhich must be, however, not greater than approximately one microsecond(approximate duration of the relaxation time of melanin) in the case ofthe bleaching of natural hair.

It has also been discovered that it is possible similarly to bleachartificially coloured hair as long as the operation is performed, as forundyed hair, by adapting the power of the laser radiation to the naturalcolour of the hair. It is only after having performed this preliminarystep, corresponding to the degradation of melanin, that the bleachingproper, corresponding to the degradation of the artificial dye, may beundertaken. In fact, the degradation of artificial dyes requires higherenergies than the degradation of melanin, such that, if it is desired todegrade the said dyes directly, the hair would be destroyed by theshattering of the keratinous fibre, as in the experiments mentionedhereinabove.

Moreover, it is known that certain old people have a "white" head ofhair which in fact has an unattractive yellowish tint. The process ofthe invention makes it possible to convert this yellowish colorationinto pure white.

The subject of the invention is therefore a process for bleaching atleast one lock or portion of lock of hair, at least partially, byirradiation of the said lock or portion of lock using a laser beam ofsufficient power to bleach the hair, characterized in that:

an area of the said portion of lock is treated by irradiation using alaser beam emitted in the form of pulses in order to bleach, at leastpartially, the hair in the said area, by degradation of the melanin inthe hair,

if required, by relative movement of the said lock with respect to thesaid laser beam, one or more other areas are treated in succession, in asimilar way, so as to treat the totality of the said portion of lock,

the above treatments are possibly repeated until the desired degree ofbleaching is obtained for the said lock or portion of lock,

the operation is performed with laser radiation of sufficient power todeliver, per pulse, an energy density of 0.1 to 1.2 J/cm²,

and the said chosen energy density is not greater than a threshold abovewhich the keratinous fibre of the hair is damaged, the said thresholdbeing lower the darker the natural colour of the hair to be treated.

It is known that a laser is essentially composed of an active mediumrendered amplifying by a pumping mechanism delivering energy to theatoms in a selective way, the said active medium being contained in aresonant cavity. The active medium is then capable of emitting asubstantially monochromatic, polarized and coherent light beam. Becauseof this coherence, a laser beam concentrates a markedly greater energythan that of radiation emitted by a conventional light source.

Certain lasers, especially those with a solid-state active medium, arecapable of emitting laser radiation in the form of very short pulses(generally between one femtosecond and one microsecond). Theconcentration of energy into such short time intervals gives the laserpulse a considerable power, called peak power. In the process of theinvention, lasers are preferably used which allow production ofcontrolled pulses. For example, it is possible to use ruby lasers orlasers for which the active medium contains ions of rare earths or ofactinides, for example a neodymium-type laser. The construction of suchlasers is well known. The active ions may be inserted into a crystallinematrix, such as yttrium aluminium garnet (YAG for short), or into anamorphous matrix such as a glass. The pulse repetition frequency isadjusted using a pumping flashlamp. The available energy may be adjustedusing conventional systems, especially polarizers.

Preferably, lasers are used which emit in the near ultraviolet, in thevisible or in the near infrared, for example at wavelengths of 300 to1100 nm. For example, it is possible to use a neodymium-YAG laser whichemits at 1.06 μm, possibly with a frequency multiplier which makes itpossible, for example, to obtain 532 nm wavelength emission (double thefrequency) or 355 nm wavelength emission (three times the frequency).

The peak-power/pulse-duration pair (for example the peak power of thelaser beam for a given pulse duration) may be easily determined bytaking into account the conditions concerning the energy density perpulse, as a function of the natural colour of the hair, even if dyedhair is involved. More precisely, care must be taken not to exceed amaximum energy density per pulse which is of the order of:

0.35 J/cm² for very dark brown hair (of the Japanese or Mexican type),

0.4 J/cm² for dark chestnut hair,

0.5 J/cm² for light chestnut hair,

0.7 J/cm² for dark blond hair,

1.2 J/cm² for light blond hair.

The various data supplied hereinabove relating to the energy densitywere established for a radiation of 532 nm wavelength. When thewavelength used is different, a correction factor ##EQU1## should beapplied, as is explained in more detail in the experimental parthereinbelow.

Moreover, it is recalled that the various hair colours may be definedobjectively using the luminance (L), according to the C.I.E. system ofcolorimetric coordinates (L,a,b). In the present application, the haircolours mentioned correspond to the luminance ranges mentionedhereinbelow:

    ______________________________________                                        Hair type             L                                                       ______________________________________                                        Japanese or Mexican   less than 18                                            Dark chestnut         18-20                                                   Light chestnut        22-24                                                   Dark blond            28-35                                                   Light blond           45-52                                                   ______________________________________                                    

The process described hereinabove, which corresponds to at least partialbleaching by degradation of the melanin in the hair, must be performed,in all cases, even if hair dyed using a colouring agent is treated and,in this latter case, the bleaching process comprises an additional stepof irradiation of the hair, similar to the step described hereinabove,but by laser radiation delivering a higher energy density, sufficient todestroy or degrade the colouring agent; this energy density isespecially at least equal to 0.8 J/cm². It is generally less than 2J/cm² at 532 nm.

In order to implement the preliminary step of degradation of themelanin, all that is required is to know the natural colour of the dyedhair to be treated and then irradiation conditions are applied which aresuitable for the hair having this natural colour, the said conditionshaving been determined beforehand, once and for all, by simple routineexperiments.

The duration of the pulses may range, for example, from 10 picosecondsto 100 nanoseconds.

The process of the invention obviously requires bleaching the head ofhair in locks, by successively irradiating areas of the said lock.Generally, the irradiation area may vary within the range 0.1-2 cm².

The process of the invention is therefore particularly well suited forobtaining highlighted heads of hair. In order to treat the areas to bebleached in succession, by relative movement of a lock with respect tothe laser beam, it is possible to move the lock with respect to theapparatus used for the treatment, or vice versa, and/or to vary thedirection of the laser beam periodically so as to perform successivescans of the treated area. This periodic variation in the direction ofthe laser beam may be achieved, for example, using an oscillatingmirror.

It has been observed that, when bleaching is performed by laser shots insequence, the hair tends to heat up locally. In order for this localheating not to be able to damage the hair, it is advisable to limit thepulse repetition frequency and/or to carry out sufficient relativemovements of the treated lock of hair with respect to the laser beam soas to prevent cumulative heating, after which it is possible to returnto a previously treated area, having had time to cool down sufficiently,in order to complete the treatment, and so on. In practice, it is easyto determine a suitable pulse repetition frequency and/or an appropriatespeed of movement of the lock of hair with respect to the laser beamsimply by routine experiments, the said suitable frequency and/or thesaid appropriate speed being those for which heating potentiallydamaging to the hair is not observed. For example, it is possible tochoose a pulse repetition frequency which can range from 5 to 50 Hz,especially from 10 to 20 Hz.

The treated hair may be dry or wet.

In order to be able to bleach the treated lock of hair under goodconditions, it is preferable to arrange this lock in the form of aribbon of hair and it is then possible to bleach the hair in the treatedarea by irradiating at least one of the faces of the said ribbon.Preferably, the thickness of the ribbon of hair corresponds to thethickness of approximately 3 to 20 superposed hairs.

According to a particular embodiment, the process of the invention ischaracterized in that:

the operation is performed using a treatment device which includes areceptacle for the lock of hair to be treated, the surface of the saidreceptacle having an orifice for the exit of the said laser beam,

the hair of the said lock, spread out in the form of a ribbon, isapplied, over at least part of its length, to the surface of the saidreceptacle so that an area to be treated is opposite the said orifice,

irradiation of the said area is then carried out,

and, by relative movements of the said lock with respect to the laserbeam, irradiation of the other areas to be treated is carried out insuccession.

Devices allowing such an implementation will be described hereinbelow.With these devices, the relative movements of the lock with respect tothe laser beam may be achieved by relative movements of the lock withrespect to the said receptacle and/or by periodic variations in thedirection of the laser beam, as indicated previously.

One of the advantages of the process of bleaching of hair by irradiationwith a laser beam is that it is possible to monitor continuously thebleaching produced and to stop the treatment at the chosen degree ofbleaching.

As indicated hereinabove, the main advantage of laser irradiationbleaching is that the hair is not degraded and the mechanical andphysico-chemical properties that it had before treatment are preserved.Here there is a considerable advantage since it is possible to perform,on the hair bleached in this way, any other cosmetic treatments withouttaking special precautions.

Another subject of the invention is a device for implementing thehair-bleaching process as defined previously. This device ischaracterized in that it includes:

a body equipped with a receptacle, the said receptacle being intended toserve as a housing, over at least part of the length of the hair, for alock of hair to be treated, the lock being spread out in the form of aribbon;

and means intended to convey a laser beam so as to irradiate at leastone area of a lock of hair arranged in the said receptacle.

In particular embodiments, the device of the invention may also have thefollowing characteristics, taken in isolation or, if required, incombination:

the said receptacle includes a wide-bottomed groove, making it possibleto spread out the said ribbon on the said bottom;

the said groove may be associated with a disengageable piece ofcooperating shape, capable of being inserted into the said groove,leaving, between the said piece and the bottom of the groove, a spaceforming a housing for the said ribbon; the said piece be disengaged, forexample, by actuating a lever which makes it possible to introduce thelock to be treated into the receptacle or to remove it therefrom; thebottom of the said groove and/or one face of the said piece opposite thesaid bottom may have an orifice for the exit of a laser beam onto thearea to be irradiated;

in another embodiment, the said receptacle includes a groove in the formof a narrow slot emerging at the surface of the said body and having adepth sufficient to allow insertion of the said ribbon over the totalityof its width; in a way similar to that mentioned hereinabove for thefirst embodiment, at least one of the faces opposite the said narrowslot may have an orifice for the exit of a laser beam.

Of course, the receptacle must form a light-tight confined space inorder to prevent the laser radiation from causing damage to the user orto his clients.

The invention will now be described with reference to the appendeddrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a first embodiment of the device of theinvention, which includes, at its end, a receptacle in the form of awide-bottomed groove and a cooperating piece which can be actuated by alever;

FIG. 2 is a partial view from above of the end, carrying the receptacle,of the device of FIG. 1;

FIG. 3 illustrates diagrammatically the mode of use of the device ofFIG. 1;

FIG. 4 represents a diagrammatic sectional view of a second embodimentof the device, with a receptacle in the form of a narrow slot;

FIG. 5 is a vertical longitudinal sectional view of the device of FIG.4;

and FIG. 6 shows diagrammatically the mode of use of the device of FIG.4.

FIG. 1 shows that the device includes a partially hollow elongate body(1) whose front end (1a) of smaller cross-section comprises a receptaclehaving the shape of a flat-bottomed groove (2). A conduit (3) for thelaser beam emerges in the bottom of the groove (2) after being sharplyreflected by means of the mirror (4), and forms an exit window (3a) atthe surface of the wall (2). The dotted lines (3b) show diagrammaticallythe propagation of the laser beam inside the body (1) or may represent awaveguide.

A cooperating piece (5), which can move about the axis (6), is heldengaged in the receptacle by means of return means, such as a tensionspring (not depicted), and can be disengaged by actuating the lever (7)with which the piece (5) is equipped at its rear end. The rear part (8)of the body (1) serves as a handle for the apparatus to be gripped bythe operator. In order to bleach the hair, the piece (5) is disengagedin order to be able to arrange the lock of hair (10), distributed in theform of a ribbon as indicated in FIG. 3, and then the piece (5) isallowed to re-engage in the groove. The lock therefore lies arranged inthe space between the faces (2) and (9), the laser emitter (notrepresented) is actuated and the device is moved with respect to thelock (or vice versa) in the direction indicated by the arrow in FIG. 3in order to bleach, in succession, the entire lock or portion of lock tobe treated. It is preferable to perform movements which are not tooslow, for example of the order of 0.1-5 centimeters per second and to dothis in successive passes, to treat the hair to be bleached severaltimes, thereby making it possible to monitor very easily the progress ofthe bleaching, under good safety conditions. However, it is alsopossible to use slower speeds of movement or discontinuous movements,for example in combination with a suitable low pulse frequency.

The body of the device my be made of any appropriate material, forexample of light metal such as aluminium or of plastic.

The device represented in FIGS. 4 and 5 comprises an elongate body (11)of which only the front part has been represented, the rear part, notrepresented, forming the handle. It may be seen that the end of the body(11) splits into two branches (11a) and (11b) separated by a slot whoseopposite faces (12) and (13) constitute a housing for a lock of hair(14) arranged as indicated in FIG. 6. As in the first embodiment, alaser channel (15) emerges on the face (13) of the slot, after havingbeen reflected by the mirror (16). This device is used in a similar wayto the previous one.

The units for controlling the laser beam and the cooling circuit can beinstalled on the device or in a separate control unit which may possiblybe foot-actuated. It is also possible to provide devices for slaving thelaser power as a function of the colour of the lock to be treated, itbeing possible for this slaving to be carried out automatically afterthe colour has been read by an appropriate detector.

The following examples illustrate the invention.

EXAMPLE 1

In this example and in the following examples, 0.25 g locks of hair,having a length of 20 cm, are used.

The apparatus used is an apparatus of the type represented in FIG. 1.

The laser radiation source is a Surelite Continuum laser: wavelength 532nm; shot frequency 1 Hz; beam diameter 5 mm; pulse duration 4 ns.

With this equipment, the ranges of optimal bleaching, depending on thecolour of the hair to be treated, have been studied.

The ranges of energy per cm² for one pulse are those which can be usedfor bleaching hair effectively.

Below the minimum value, there is no appreciable bleaching. Above themaximum value, the fibre of an individual hair shatters or cracks up(the damage is visible, depending on its size, with a binocularmagnifier, a microscope or an electron microscope).

The results are summarized in Table (I) below:

    ______________________________________                                                          energy/cm.sup.2 for 1 pulse                                 Hair              (in J/cm.sup.2)                                             ______________________________________                                        Japanese          0.2 to 0.35                                                 Dark chestnut     0.2 to 0.4                                                  Light chestnut    0.15 to 0.5                                                 Dark blond        0.15 to 0.7                                                 Light blond       0.1 to 1.2                                                  ______________________________________                                    

Moreover, the absorption of luminous energy by melanin varies with thewavelength--it decreases when the wavelength increases, in such a waythat the hair withstands, without degradation, a higher incident energydensity when the wavelength increases. The experimental study has shownthat the maximum energy density which can be withstood by the hair,without the keratinous fibre shattering, for radiation of wavelength λ,is substantially that indicated in the above table, multiplied by afactor ##EQU2## where λ is expressed in nanometers. This law ofvariation with wavelength is also valid for the relationship between theincident energy density and the efficiency of the bleaching--the energydensity capable of bleaching hair of a given type, for the wavelength λ,is substantially equal to the energy density enabling similar bleachingto be achieved with radiation of 532 nm wavelength, multiplied by thesaid factor ##EQU3##

For artificially coloured hair, it is necessary to use quite high energydensities, generally at least equal to 0.8 J/cm² per pulse. If the hairhas been coloured without prior bleaching, its natural colour must betaken into account. For example, if the natural colour of the hair waslight chestnut, it is necessary firstly to use an energy density notgreater than 0.5 J/cm² (see Table 1 above) in order to bleach themelanin. It is only afterwards that it will be possible to use a higherenergy density (1 J/cm² or more) in order to destroy the artificial dye.If this high energy density were to be applied at the outset, the hairwould shatter.

EXAMPLE 2

The procedure is as above, but with a BMI laser having the followingcharacteristics: wavelength 523 nm; shot frequency 10 Hz; beam diameter3 mm; pulse duration 30 ps.

The peak power per unit area, corresponding to optimum bleaching fordark chestnut hair, is of the order of 9.5 GW/cm², i.e. an energy perunit area of 0.28 J/cm².

Furthermore, it has been observed that laser irradiation leaves thealkaline solubility and the cysteic-acid content of bleached hairvirtually-unaltered compared to the hair before bleaching, whereas theseare greatly increased in the case of bleaching by chemical route.

We claim:
 1. A process for bleaching at least one area of a hair lockwithout appreciable degradation of the keratinous fibers thereof,comprising:irradiating said at least one area with a laser beam emittedin the form of pulses in order to bleach said at least one area bydegradation of melanin contained in said fiber, said irradiating beingperformed with laser radiation of sufficient power to deliver an energydensity per pulse of 0.1 to 1.2 J/cm², for a wavelength of 532 nm, saidenergy density being multiplied by a correction factor equal to λ/532when the radiation has a wavelength of λ nm other than 532 nm; and saidenergy density being not greater than a threshold above which saiddegradation of the keratinous fibers occur.
 2. The process according toclaim 1, further comprising moving said laser beam relative to said hairlock.
 3. The process according to claim 1, wherein said energy densityper pulse has a maximum of0.35 J/cm² for black hair, 0.4 J/cm² for darkchestnut hair, 0.5 J/cm² for light chestnut hair, 0.7 J/cm² for darkblond hair, 1.2 J/cm² for light blond hair,for a wavelength of 532 nm,said maximum being multiplied by a correction factor equal to λ/532 whenthe radiation used has a wavelength of λ nm, other than 532 nm.
 4. Theprocess according to claim 1, wherein said energy density per pulse, inJ/cm² for a wavelength of 532 nm, is in the range of0.2-0.35 for darkbrown hair, 0.2-0.4 for dark chestnut hair, 0.15-0.5 for light chestnuthair, 0.15-0.7 for dark blond hair, 0.1-1.2 for light blond hair,saidranges being multiplied by a correction factor equal to: ##EQU4## whenthe radiation used has a wavelength λ nm other than 532 nm.
 5. Theprocess according to claim 1, wherein said hair lock is arranged, priorto said irradiation, in the form of a ribbon,said irradiating beingperformed on at least one face of said ribbon.
 6. The process accordingto claim 1, wherein said treatment comprises the use of a device whichincludes:(a) a receptacle for a hair lock to be irradiated, saidreceptacle being provided with a surface having an orifice for the exitof the said laser beam, the hair lock being spread out, in the form of aribbon, over at least part of its length, onto a surface of the saidreceptacle so that an area to be irradiated is opposite the orifice, (b)irradiation means to irradiate said area, and (c) movement means for therelative movement of the said hair lock with respect to the laser beam.7. The process according to claim 6, wherein said relative movement ofsaid hair lock includes relative movement of said hair lock with respectto said receptacle.
 8. The process according to claim 6, wherein saidrelative movement is obtained by periodically varying the direction ofthe laser beam so as to perform scanning of the area to be irradiated.9. The process according to claim 7, comprising emitting said pulses ata pulse frequency of from 5 to 50 Hz.
 10. A process for bleaching atleast one area of a hair lock which is artificially dyed with a coloringagent, comprising:a) irradiating said at least one area with a laserbeam emitted in the form of pulses in order to bleach said at least onearea by degradation of melanin contained in said fiber, said irradiatingbeing performed with laser radiation of sufficient power to deliver anenergy density per pulse of 0.1 to 1.2 J/cm², for a wavelength of 532nm, said energy density being multiplied by a correction factor equal toλ/532 when the radiation has a wavelength of λ nm other than 532 nm,said energy density being not greater than a threshold above which saiddegradation of the keratinous fibers occurs; and b) subsequentlyirradiating said at least one area, as in a) above, but with a secondenergy density, per pulse, which is sufficient to destroy or degradesaid coloring agent without degrading said keratinous fibers.
 11. Theprocess according to claim 10, wherein said second energy density is atleast equal to 0.8 J/cm² per pulse for 532 nm.